According to the US Centers for Disease Control and Prevention, two doses of the MMR (measles, mumps and rubella) vaccine are 97% effective at preventing measles, while one dose is 93% effective. It is uncommon for someone who is fully vaccinated to develop measles, although the first breakthrough case of 2025 was recently detected in Colorado.

The number of measles cases in the U.S. has reached a 33-year record high, years after it was officially eliminated in the country, prompting public health experts to sound the alarm that other diseases could experience a similar resurgence.